In 2002, Robert A. Levy, a Senior Fellow at the Cato Institute, began vetting plaintiffs with Clark M. Neily III for a planned Second Amendment lawsuit that he would personally finance. Although he himself had never owned a gun, as a Constitutional scholar and believer in individual rights, he had an academic interest in the subject and wanted to model his campaign after the legal strategies of Thurgood Marshall, who had successfully led the challenges that overturned school segregation.[2] They aimed for a group that would be diverse in terms of age, race, and economic background. They eventually picked Shelly Parker, Tom Palmer, Gillian St. Lawrence, Tracey Ambeau, George Lyon and Dick Heller. Before the case, Levy knew only Tom Palmer, a colleague from the Cato Institute, and none of the six knew each other.[3]

In February 2003, the six residents of Washington, D.C. filed a lawsuit in the United States District Court for the District of Columbia, challenging the constitutionality of provisions of the Firearms Control Regulations Act of 1975, a local law enacted pursuant to District of Columbia home rule. This law restricts residents from owning handguns, excluding those grandfathered in by registration prior to 1975 and those possessed by active and retired law enforcement officers. The law also requires that all firearms including rifles and shotguns be kept "unloaded and disassembled or bound by a trigger lock."[4] The District Court dismissed the lawsuit.

On appeal, the U.S. Court of Appeals for the D.C. Circuit reversed the dismissal in a 2-1 decision. The Court of Appeals struck down provisions of the Firearms Control Regulations Act as unconstitutional. Judges Karen L. Henderson, Thomas B. Griffith and Laurence H. Silberman formed the Court of Appeals panel, with Senior Circuit Judge Silberman writing the court's opinion and Circuit Judge Henderson dissenting.

The court's opinion first addressed whether appellants have standing to sue for declaratory and injunctive relief in section II (slip op. at 5–12). The court concluded that of the six plaintiffs, only Heller—who applied for a handgun permit but was denied—had standing.

The court then held that the Second Amendment "protects an individual right to keep and bear arms", saying that the right was "premised on the private use of arms for activities such as hunting and self-defense, the latter being understood as resistance to either private lawlessness or the depredations of a tyrannical government (or a threat from abroad)." They also noted that though the right to bear arms also helped preserve the citizen militia, "the activities [the Amendment] protects are not limited to militia service, nor is an individual's enjoyment of the right contingent upon his or her continued or intermittent enrollment in the militia." The court determined that handguns are "Arms" and concluded that thus they may not be banned by the District of Columbia; however, they said that Second Amendment rights are subject to reasonable restrictions.

The court also struck down the portion of the law that requires all firearms including rifles and shotguns be kept "unloaded and disassembled or bound by a trigger lock." The District argued that there is an implicit self-defense exception to these provisions, but the D.C. Circuit rejected this view, saying that the requirement amounted to a complete ban on functional firearms and prohibition on use for self-defense:[5]

“ Section 7-2507.02, like the bar on carrying a pistol within the home, amounts to a complete prohibition on the lawful use of handguns for self-defense. As such, we hold it unconstitutional.

This case featured involvement by groups for and against expanded gun rights. The National Rifle Association (NRA) was initially not supportive of the case because it feared it might not be successful. The NRA later reconciled with the plaintiffs. The Brady Campaign to Prevent Gun Violence lobbied to have DC gun laws changed so the case would be moot and not eligible to be heard by the Supreme Court.

Attorney Alan Gura, in a 2003 filing, used the term "sham litigation" to describe the NRA's attempts to have Parker (aka Heller) consolidated with its own case challenging the D.C. law. Gura also stated that "the NRA was adamant about not wanting the Supreme Court to hear the case".[34] These concerns were based on NRA lawyers' assessment that the justices at the time the case was filed might reach an unfavorable decision.[35] Cato Institute senior fellow Robert Levy, co-counsel to the Parker plaintiffs, has stated that the Parker plaintiffs "faced repeated attempts by the NRA to derail the litigation."[36]

Wayne LaPierre, the NRA’s chief executive officer, confirmed the NRA's misgivings. "There was a real dispute on our side among the constitutional scholars about whether there was a majority of justices on the Supreme Court who would support the Constitution as written,"